/Engine/Plugins/Importers/USDImporter/Source/USDStage/Public/USDStageActor.h
Returns the root layer identifier of the currently isolated stage if we're in isolated mode, and the empty string otherwise.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="USD", Meta=(CallInEditor="true")) [FString](API\Runtime\Core\Containers\FString) GetIsolatedRootLayer() const